My invention relates to the construction of the propulsion system of a vehicle. More particularly, the invention relates to the engine and drive train construction of small off-road military vehicles.
My propulsion system includes a relatively small internal combustion engine, a pump driven by the engine, at least one hydraulic motor driven by the pump, and at least one vehicle wheel driven by the hydraulic motor. The flow volume of the pump per revolution of the engine is controlled by a conventional swash plate in the pump. The swash plate is itself controlled by a lever, such as a foot pedal, mechanically linked to the swash plate. On the drive shaft connecting the engine and pump is a flywheel whose moment of rotational inertia is varied by radially translating weights on the flywheel. Under normal vehicle operating conditions, the weights are translated outward whereby rotational energy is stored in the flywheel. When more power is momentarily needed than the engine can provide, the weights on the flywheel translate inwardly so the flywheel imparts rotational energy to the pump through the drive shaft.
The invention includes a means for maintaining the engine at a relatively constant speed within the most efficient r.p.m. range for the engine. Vehicle speed and direction is varied by controlling the flow from the pump and thereby controlling the speed and direction of the hydraulic motor. The propulsion system has an override mode wherein the engine speed is set at a new, higher level when the foot pedal exceeds a given range of movement.
My invention is particularly useful in a small four-wheel-drive vehicle for accompanying foot soldiers across rough terrain with their equipment and supplies. This vehicle, commonly referred to as a mule, is preferably as light as possible so that it may be flown to the area of use by a cargo plane and parachuted directly into that area. Light vehicle weight not only increases air transportability of the mule but also reduces the impact shock it receives during a parachute landing. Light vehicle weight also increases the net payload which the mule can carry. Mules are preferably of simple and easily repairable construction since they often used in remote areas where repair facilities are not available and since the foot soldiers using the mules are typically not mechanically trained. From a logistical point of view, a simpler vehicle is more easily supplied and kept running in its field of operation.
As applied to the mule, my invention is a propulsion system which will reduce vehicle weight by using a smaller engine than is conventionally thought necessary. Vehicle weight and complexity is lessened by eliminating the torque transferring shaft between the vehicle axles and by eliminating differential gearing in the drive train. I estimate that the weight of mules used by the U.S. Army (approximately 960 lbs.) can be reduced by 300 to 400 lbs. with the propulsion system described herein. In one of the embodiments, it is possible to eliminate the steering mechanism on the U.S. Army mules to further lighten them and simplify their construction.